System for reduction of a magnetic fringe field of a magnetic resonance imaging device

ABSTRACT

A magnetic resonance imaging (MRI) system is provided. The MRI system can include a magnetic field device to generate a magnetic field within a measurement volume and to generate a magnetic fringe field external to the measurement volume. The MRI system can include a ferromagnetic housing to envelop the magnetic field device. The housing can have a first portion and a second portion, where thickness of the first portion is different from thickness of the second portion. The MRI system can include a plate having a plate opening and positioned external to the housing at a predetermined distance from the housing. In some embodiments, the magnetic fringe field generated by the MRI system can be asymmetric with respect to a center of the measurement volume.

FIELD OF THE INVENTION

Generally, the present invention relates to the field of magneticresonance imaging systems. More particularly, the present inventionrelates to shielding of a magnetic fringe field.

BACKGROUND OF THE INVENTION

Typically, magnetic resonance imaging (MRI) systems can generate amagnetic fringe field external to a measurement volume of the MRIsystem. The magnetic fringe field can, for example, interfere withelectronic equipment in the fringe field and/or attract metallic objectspositioned in a vicinity of the MRI system. The metallic objectsattracted by the magnetic fringe field can, for example, enter into themeasurement volume of the MRI system, thereby endangering a patientundergoing a MRI scan. Accordingly, MRI devices are typically deployedin a dedicated MRI room.

Deployment of MRI systems in a dedicated room can be expensive and canrequire dedicated space within a hospital, doctor's office and/or otherinstitution using MRI systems. Therefore, it can be desirable to deployMRI systems without requiring a dedicated MRI room.

SUMMARY OF THE INVENTION

There is thus provided, in accordance with some embodiments of theinvention, a magnetic resonance imaging (MRI) system, the systemincludes: a magnetic field device to generate a magnetic field within ameasurement volume and to generate a magnetic fringe field external tothe measurement volume, wherein the measurement volume is to accommodateat least a portion of a patient; a ferromagnetic housing to envelop themagnetic field device, the housing having a first portion and a secondportion, wherein thickness of the first portion is different fromthickness of the second portion; and a plate, having a plate opening,positioned external to the housing at a predetermined distance from thehousing, wherein the plate opening is aligned with a correspondinghousing opening in the housing to allow insertion of at least a portionof the patient therethrough; wherein the generated magnetic fringe fieldis asymmetric.

In some embodiments, at least one of the thickness of the second portionof the housing, the distance between the plate and the housing anddimensions of the plate are predetermined to reduce the magnetic fringefield at the plate opening to a predetermined value.

In some embodiments, the second portion of the housing comprises thehousing opening.

In some embodiments, the thickness of the second portion of the housingis greater compared to the thickness of the second portion of thehousing.

In some embodiments, the plate comprises a metal alloy, the metal alloycomprises at least one of: copper, iron, aluminum, ferromagneticmaterial, paramagnetic material or any combination thereof.

In some embodiments, the plate is coupled to the housing using anon-ferromagnetic and a non-paramagnetic material.

In some embodiments, the system is positioned within a desired room andwherein the plate is coupled to at least one of: a floor of the room, aceiling of the room or any combination thereof.

In some embodiments, a shape of the plate is selected from the groupconsisting of: a square, a rectangular, and an oval.

In some embodiments, the plate has a thickness of 12 millimeters.

In some embodiments, dimensions of the plate and the distance of theplate from the housing are predetermined based on a desired magneticfringe field at the plate opening.

There is thus provided, in accordance with some embodiments of theinvention, a ferromagnetic housing to envelop a magnetic field device,the housing includes: a first portion and a second portion, whereinthickness of the first portion is different from thickness of the secondportion; and a housing opening to allow insertion of at least a portionof the patient therethrough into a measurement volume of the magneticfield device.

In some embodiments, the thickness of the second portion of the housingis predetermined to reduce a magnetic fringe field in a region adjacentto the second portion.

In some embodiments, the second portion of the housing comprises thehousing opening.

In some embodiments, the thickness of the second portion of the housingis greater compared to the thickness of the second portion of thehousing.

It will be appreciated that, for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, can beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIGS. 1A-1B schematically illustrate a magnetic resonance imaging (MRI)system according to some embodiments of the invention;

FIGS. 2A-2B schematically illustrate a magnetic resonance imaging (MRI)system, including an asymmetric housing, according to some embodimentsof the invention; and

FIGS. 3A-3B schematically illustrate a magnetic resonance imaging (MRI)system, including an asymmetric housing and a plate positioned at apredetermined distance from the housing, according to some embodimentsof the invention.

It will be appreciated that, for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the present inventionare described. For purposes of explanation, specific configurations anddetails are set forth in order to provide a thorough understanding ofthe present invention. However, it will also be apparent to one skilledin the art that the present invention may be practiced without thespecific details presented herein. Furthermore, well known features mayhave been omitted or simplified in order not to obscure the presentinvention. With specific reference to the drawings, it is stressed thatthe particulars shown are by way of example and for purposes ofillustrative discussion of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

Before at least one embodiment of the invention is explained in detail,it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is applicable to other embodiments that may bepracticed or carried out in various ways as well as to combinations ofthe disclosed embodiments. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

Reference is now made to FIGS. 1A-1B, which schematically illustrate amagnetic resonance imaging (MRI) system 100 according to someembodiments of the invention.

Illustrations 100 a and 100 b in FIG. 1A show a perspective view and aside cross-sectional view of the MRI system, respectively. Illustrations100 c and 100 d in FIG. 1B show a top view and a side view of the MRIsystem 100, respectively, and a region 190 surrounding the MRI system100, in which the magnetic fringe field is greater than a predeterminedvalue (e.g., a magnetic field value based on the magnetic field strengththat can cause metallic objects to move towards the MRI system 100).

The MRI system 100 can include a magnetic field device 110. The magneticfield device 110 can generate a magnetic field within a measurementvolume 112 and can generate a magnetic fringe field external to themeasurement volume 112. The magnetic field device can include multiplemagnets 114 (e.g., permanent magnets). The magnetic field device caninclude multiple ferromagnetic elements 116 (e.g., pole pieces) that canbe positioned adjacent to at least one of the multiple magnets 114(e.g., as shown in FIG. 1A). In some embodiments, the measurement volume112 is adapted to accommodate at least a portion (e.g., a head) of apatient (not shown).

The MRI system 100 can include a housing 120 that can be made of aferromagnetic material. The housing 120 can include a proximal end 120 aand a distal end 120 b along a longitudinal axis 102 of the MRI system100. The housing 120 can envelope the magnetic field device 110. Thehousing 120 can include a housing opening 122 at the proximal end 120 a.The housing opening 122 can enable insertion of the at least portion ofthe patient (e.g., the head) within the measurement volume 112 of themagnetic field device 110.

In some embodiments, the housing 120 includes additional openings 123,for example, a first additional opening 123 a, a second additionalopening 123 b and/or a third additional opening 123 c. The firstadditional opening 123 a can be positioned at the distal end 120 b ofthe housing 120 and/or can be coaxially aligned with the housing opening122 (e.g., as shown in FIG. 1A). The second additional opening 123 band/or the third additional opening 123 c can be positioned at variouslocations of the housing 120, for example as shown in FIG. 1A. Theadditional openings 123 can, for example, reduce a weight of the housing120.

In some embodiments, the housing opening 122 has greater diameter ascompared to additional openings 123. In some embodiments, the housing120 includes the housing opening 122 without additional openings 123.

The MRI system 100 can generate magnetic field within the measurementvolume 112 of the magnetic field device 110. The magnetic field measuredat a center 112 a of the measurement volume 112 can range, for example,between 4900-5100 Gauss. The MRI system 100 can generate magnetic fringefield in a region 190 surrounding the MRI system 100. The region 190 canindicate a region in which the magnetic fringe field is above apredetermined value, for example 10 Gauss. The magnetic fringe fieldgenerated by the MRI system 100 can be substantially symmetric withrespect to the center 112 a of the measurement volume 112 (e.g., asshown in FIG. 1B). The magnetic fringe field measured on thelongitudinal axis 102 at a predetermined distance of 1000 mm from thecenter 112 a of the measurement volume 112 can range, for example,between 35-45 Gauss

Reference is now made to FIGS. 2A-2B, which schematically illustrate amagnetic resonance imaging (MRI) system 200, including an asymmetrichousing 220, according to some embodiments of the invention.

Illustrations 200 a and 200 b in FIG. 2A show a perspective view and aside cross-sectional view of the MRI system, respectively. Illustrations200 c and 200 d in FIG. 2B show a top view and a side view of the MRIsystem 200, respectively, and a region 290 surrounding the MRI system200, in which the magnetic fringe field is greater than a predeterminedvalue.

The MRI system 200 can include a magnetic field device 210. The magneticfield device 210 can generate a magnetic field within a measurementvolume 212 and can generate a magnetic fringe field external to themeasurement volume 212. In various embodiments, the magnetic fielddevice 210 and/or the measurement volume 212 are identical to themagnetic field device 110 and the measurement volume 112, respectively,as described above with respect to FIGS. 1A-1B.

The magnetic field device 210 can include multiple magnets 214 (e.g.,permanent magnets) and/or multiple ferromagnetic elements 216 (e.g.,pole pieces) that can be positioned adjacent to at least one of themultiple magnets 214 (e.g., as shown in FIG. 2A). In variousembodiments, magnets 214 and/or ferromagnetic elements 216 are identicalto magnets 114 and ferromagnetic elements 116, respectively, asdescribed above with respect to FIGS. 1A-1B.

The MRI system 200 can include a housing 220 that can be made of aferromagnetic material. The housing 220 can include a proximal end 220 aand a distal end 220 b along a longitudinal axis 202 of the MRI system200. The housing 220 can envelope the magnetic field device 210. Thehousing 220 can include a housing opening 222 at the proximal end 220 a.The housing opening 222 can enable insertion of at least a portion of apatient (e.g., a head) within the measurement volume 212 of the magneticfield device 210. In some embodiments, the housing opening 222 isidentical to the housing opening 122, as described above with respect toFIGS. 1A-1B. In various embodiments, the housing 220 includes additionalopenings 223 (e.g., a first additional opening 223 a, a secondadditional opening 223 b and/or a third additional opening 223 c) thatcan be identical to the additional openings 123 (e.g., the firstadditional opening 123 a, the second additional opening 123 b and/or thethird additional opening 123 c), as described above with respect toFIGS. 1A-1B. In some embodiments, the housing 220 includes the housingopening 222 without additional openings 223.

The housing 220 can include a first portion 224 and/or a second portion226, where a thickness of the first portion 224 can be different from athickness of the second portion 226 (e.g., as shown in FIG. 2A). In someembodiments, the second portion 224 includes at least a portion of theproximal end 220 a of the housing 220 (e.g., around the housing opening222). In various embodiments, the thickness of the first portion 224and/or the thickness of the second portion 226 are predetermined toreduce the magnetic fringe field external to the housing 220. In someembodiments, the thickness of the second portion 226 is greater than thethickness of the first portion 224 (e.g., as shown in FIG. 2A). Forexample, the thickness of the first portion 224 can range between 45-55mm and/or the thickness of the second portion 226 can range between90-110 mm.

In various embodiments, the second portion 226 includes at least aportion of the proximal end 220 a (e.g., around the housing opening 222)and/or at least a portion of at least one of: distal end 220 b and/orside portions of housing 220 (e.g., around at least some of theadditional openings 223). In various embodiments, housing 220 includestwo (e.g., the first portion 224 and the second portion 226) or moreportions (not shown), where each of the portions has differentthickness.

The MRI system 200 can generate magnetic field within the measurementvolume 212 of the magnetic field device 210. The magnetic field measuredat a center 212 a of the measurement volume 212 can range, for example,between 4900-5100 Gauss. The MRI system 200 can generate magnetic fringefield in a region 290 surrounding the MRI system 200. The region 290 canindicate a region in which the magnetic fringe field is above apredetermined value, for example 10 Gauss. The magnetic fringe fieldgenerated by the MRI system 200 can be asymmetric with respect to thecenter 212 a of the measurement volume 212. For example, the region 290can include a zone 292 (e.g., indicated by a dashed pattern in FIG. 2B)positioned adjacent to the second portion 226 at the proximal end 220 aof the housing 220, in which the magnetic fringe field can be smaller ascompared to the magnetic fringe field in corresponding opposite zone ofthe region 290 poisoned adjacent to the distal end 220 b of the housing220. The magnetic fringe field measured on the longitudinal axis 202 ata predetermined distance of 1000 mm from the center 212 a of themeasurement volume 212 can range, for example, between 15-25 Gauss.

Reference is now made to FIGS. 3A-3B, which schematically illustrate amagnetic resonance imaging (MRI) system 300, including an asymmetrichousing 320 and a plate 330 positioned at a predetermined distance fromthe housing 320, according to some embodiments of the invention.

Illustrations 300 a and 300 b in FIG. 3A show a perspective view and aside cross-sectional view of the MRI system, respectively. Illustrations300 c and 300 d in FIG. 3B show a top view and a side view of the MRIsystem 300, respectively, and a region 390 surrounding the MRI system300, in which the magnetic fringe field is greater than a predeterminedvalue.

The MRI system 300 can include a magnetic field device 310. The magneticfield device 310 can generate a magnetic field within a measurementvolume 312 and can generate a magnetic fringe field external to themeasurement volume 312. In various embodiments, the magnetic fielddevice 310 and/or the measurement volume 312 are identical to themagnetic field device 110 and the measurement volume 112, respectively,as described above with respect to FIGS. 1A-1B, and/or identical to themagnetic field device 210 and the measurement volume 212, respectively,as described above with respect to FIGS. 2A-2B.

The magnetic field device 310 can include multiple magnets 314 (e.g.,permanent magnets) and/or multiple ferromagnetic elements 316 (e.g.,pole pieces) that can be positioned adjacent to at least one of themultiple magnets 314 (e.g., as shown in FIG. 3A). In variousembodiments, magnets 314 and/or ferromagnetic elements 316 are identicalto magnets 114 and ferromagnetic elements 116, respectively, asdescribed above with respect to FIGS. 1A-1B, and/or identical to magnets214 and ferromagnetic elements 216, respectively, as described abovewith respect to FIGS. 2A-2B.

The MRI system 300 can include a housing 320 that can be made of aferromagnetic material. The housing 320 can include a proximal end 320 aand a distal end 320 b along a longitudinal axis 302 of the MRI system300. The housing 320 can envelope the magnetic field device 310. Thehousing 320 can include a housing opening 322 at the proximal end 320 a.The housing opening 322 can enable insertion of at least a portion of apatient (e.g., a head) within the measurement volume 312 of the magneticfield device 310. In some embodiments, the housing opening 322 isidentical to the housing opening 122, as described above with respect toFIGS. 1A-1B, and/or identical to the housing opening 222, as describedabove with respect to FIGS. 2A-2B. In various embodiments, the housing320 includes additional openings 323 (e.g., a first additional opening323 a, a second additional opening 323 b and/or a third additionalopening 323 c) that can be identical to the additional openings 123(e.g., the first additional opening 123 a, the second additional opening123 b and/or the third additional opening 123 c), as described abovewith respect to FIGS. 1A-1B, and/or identical to the additional openings223 (e.g., the first additional opening 223 a, the second additionalopening 223 b and/or the third additional opening 223 c), as describedabove with respect to FIGS. 2A-2B. In some embodiments, the housing 320includes the housing opening 322 without additional openings 323.

The housing 320 can include a first portion 324 and/or a second portion326, where a thickness of the first portion 324 can be different from athickness of the second portion 326 (e.g., as shown in FIG. 3A). In someembodiments, the second portion 324 includes at least a portion of theproximal end 320 a of the housing 320. In some embodiments, thethickness of the second portion 326 is greater than the thickness of thefirst portion 324 (e.g., as shown in FIG. 3A). In various embodiments,the housing 320, the first portion 324 and/or the second portion 326 areidentical to the housing 220, the first portion 224 and the secondportion 226, respectively, as described above with respect to FIGS.2A-2B. For example, the thickness of the first portion 324 can rangebetween 45-55 mm and/or the thickness of the second portion 326 canrange between 90-110 mm.

The MRI system 300 can include a plate 330. The plate 330 can bepositioned external to the housing 320 at a predetermined distance 332from the proximal end 320 a of the housing. The plate 330 can include aplate opening 334. The plate opening 334 can be aligned with the housingopening 322 to allow insertion of the at least portion of the patient(e.g., the head) therethrough into the measurement volume 312. The plate330 can be made of a metal alloy that can include at least one of:copper, iron, aluminum, ferromagnetic material, paramagnetic material orany combination thereof.

The plate 330 can be coupled to the housing 320 of the MRI system 300using, for example, a non-ferromagnetic and/or a non-paramagneticmaterial (e.g., aluminum). In various embodiments, the MRI system 300 ispositioned within a desired room and/or the plate 330 is coupled to atleast one of: a floor of the room, a ceiling of the room or anycombination thereof (not shown).

In various embodiments, the thickness of the second portion 326 of thehousing 330, dimensions of the plate 330 and/or the distance 332 betweenthe plate 330 and the proximal end 320 a of the housing 320 arepredetermined based on a desired weight of the plate and/or based on adesired magnetic fringe field at the plate opening 334. For example, thedistance 332 can range between 140-160 mm and/or the plate 330 can havea substantially rectangular shape having a height ranging between1400-1500 mm, a width ranging between 1400-1500 mm and/or a thicknessranging between 10-14 mm. In various embodiments, a shape of the plate330 is selected from the group consisting of: a square, a rectangular,and/or an oval.

The MRI system 300 can generate magnetic field within the measurementvolume 312 of the magnetic field device 310. The magnetic field measuredat a center 312 a of the measurement volume 312 can range, for example,between 4900-5100 Gauss. The MRI system 300 can generate magnetic fringefield in a region 390 surrounding the MRI system 300. The region 390 canindicate a region in which the magnetic fringe field is above apredetermined value, for example 10 Gauss. The magnetic fringe fieldgenerated by the MRI system 300 can be asymmetric with respect to acenter 312 a of the measurement volume 312. For example, the region 390can include a zone 392 (e.g., indicated by a dashed pattern in FIG. 3B)positioned adjacent to the plate 330, in which the magnetic fringe fieldcan be smaller as compared to the magnetic fringe field in correspondingopposite zone of the region 390 poisoned adjacent to the distal end 320b of the housing 320. The magnetic fringe field measured on thelongitudinal axis 302 at a predetermined distance of 1000 mm from thecenter 312 a of the measurement volume 312 and adjacent to the plate 330can range, for example, between 5-7 Gauss, while the magnetic fringefield at corresponding opposite point adjacent to the distal end 320 bof the housing 320 can range, for example, between 15-25 Gauss.

Reference is now made back to FIGS. 1-3. In various embodiments, MRIsystem that includes a housing having varying thickness (e.g., thehousing 220 of the MRI system 200, as described above with respect toFIGS. 2A-2B) generates magnetic fringe field that can be lower by ˜50%and/or reduces a region that exhibits the magnetic fringe field adjacentto a thicker portion of the housing (e.g., the zone 292 in the region290, as described above with respect to FIG. 2B) as compared to MRIsystem that includes housing having uniform thickness (e.g., the housing120 of the MRI system 100, as described above with respect to FIGS.1A-1B).

In various embodiments, MRI system that includes a housing havingvarying thickness and a plate positioned adjacent to a thicker portionof the housing (e.g., the housing 320 and the plate 330 of the MRIsystem 300, as described above with respect to FIGS. 3A-3B) reduces aregion that exhibits the magnetic fringe field adjacent to the plate(e.g., the zone 392 in the region 390, as described above with respectto FIG. 3B) and/or reduces the magnetic fringe field at a plate openingby ˜70% and ˜85% as compared to MRI system that includes housing havingvarying thickness only without a plate (e.g., the MRI system 200, asdescribed above with respect to FIGS. 2A-2B) and as compared to MRIsystem that includes housing having uniform thickness (e.g., the housing120 of the MRI system 100, as described above with respect to FIGS.1A-1B), respectively.

In some embodiments, MRI system that includes a housing having varyingthickness and a plate positioned adjacent to a thicker portion of thehousing reduces the magnetic fringe field in a region adjacent to aplate opening by ˜70% as compared to corresponding opposite regionadjacent to a distal end of the housing (e.g., the housing 320 and theplate 330 of the MRI system 300, as described above with respect toFIGS. 3A-3B).

In some embodiments, the present invention can include substantiallyreducing a magnetic fringe field at a housing opening of an MRI system,while eliminating a need for a dedicated MRI room, such that, forexample, medical equipment can be positioned adjacent to the housingopening without a risk of being attracted by the magnetic fringe fieldand/or providing a medical staff with a safe access to a patientundergoing a MRI scan.

In the above description, an embodiment is an example or implementationof the invention. The various appearances of “one embodiment”, “anembodiment”, “certain embodiments” or “some embodiments” do notnecessarily all refer to the same embodiments. Although various featuresof the invention may be described in the context of a single embodiment,the features may also be provided separately or in any suitablecombination. Conversely, although the invention may be described hereinin the context of separate embodiments for clarity, the invention mayalso be implemented in a single embodiment. Certain embodiments of theinvention may include features from different embodiments disclosedabove, and certain embodiments may incorporate elements from otherembodiments disclosed above. The disclosure of elements of the inventionin the context of a specific embodiment is not to be taken as limitingtheir use in the specific embodiment alone. Furthermore, it is to beunderstood that the invention can be carried out or practiced in variousways and that the invention can be implemented in certain embodimentsother than the ones outlined in the description above.

The invention is not limited to those diagrams or to the correspondingdescriptions. For example, flow need not move through each illustratedbox or state, or in exactly the same order as illustrated and described.Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined. While the invention hasbeen described with respect to a limited number of embodiments, theseshould not be construed as limitations on the scope of the invention,but rather as exemplifications of some of the preferred embodiments.Other possible variations, modifications, and applications are alsowithin the scope of the invention. Accordingly, the scope of theinvention should not be limited by what has thus far been described, butby the appended claims and their legal equivalents.

1. A magnetic resonance imaging (MRI) system, the system comprising: amagnetic field device to generate a magnetic field within a measurementvolume and to generate a magnetic fringe field external to themeasurement volume, wherein the measurement volume is to accommodate atleast a portion of a patient; a ferromagnetic housing to envelop themagnetic field device, the housing having a first portion and a secondportion, wherein thickness of the first portion is different fromthickness of the second portion; and a plate, having a plate opening,positioned external to the housing at a predetermined distance from thehousing, wherein the plate opening is aligned with a correspondinghousing opening in the housing to allow insertion of at least a portionof the patient therethrough; wherein the generated magnetic fringe fieldis asymmetric.
 2. The MRI system of claim 1, wherein at least one of thethickness of the second portion of the housing, the distance between theplate and the housing and dimensions of the plate are predetermined toreduce the magnetic fringe field at the plate opening to a predeterminedvalue.
 3. The MRI system of claim 1, wherein the second portion of thehousing comprises the housing opening.
 4. The MRI system of claim 1,wherein the thickness of the second portion of the housing is greatercompared to the thickness of the second portion of the housing.
 5. TheMRI system of claim 1, wherein the plate comprises a metal alloy, themetal alloy comprises at least one of: copper, iron, aluminum,ferromagnetic material, paramagnetic material or any combinationthereof.
 6. The MRI system of claim 1, wherein the plate is coupled tothe ferromagnetic housing using a non-ferromagnetic and anon-paramagnetic material.
 7. The MRI system of claim 1, wherein thesystem is positioned within a desired room and wherein the plate iscoupled to at least one of: a floor of the room, a ceiling of the roomor any combination thereof.
 8. The MRI system of claim 1, wherein ashape of the plate is selected from the group consisting of: a square, arectangular, and an oval.
 9. The MRI system of claim 1, wherein theplate has a thickness of 12 millimeters.
 10. The MRI system of claim 1,wherein the predetermined distance is 150 millimeters.
 11. The MRIsystem of claim 1, wherein dimensions of the plate and the distance ofthe plate from the housing are predetermined based on a desired weightof the plate.
 12. The MRI system of claim 1, wherein dimensions of theplate and the distance of the plate from the housing are predeterminedbased on a desired magnetic fringe field at the plate opening.
 13. Aferromagnetic housing to envelop a magnetic field device, the housingcomprising: a first portion and a second portion, wherein thickness ofthe first portion is different from thickness of the second portion; anda housing opening to allow insertion of at least a portion of thepatient therethrough into a measurement volume of the magnetic fielddevice.
 14. The MRI system of claim 13, wherein the thickness of thesecond portion of the housing is predetermined to reduce a magneticfringe field in a region adjacent to the second portion.
 15. The MRIsystem of claim 13, wherein the second portion of the housing comprisesthe housing opening.
 16. The MRI system of claim 13, wherein thethickness of the second portion of the housing is greater compared tothe thickness of the second portion of the housing.